Colloquium

Imaging the Structure and Dynamics near the Event Horizon of a Black Hole

Speaker:Michael Johnson, Harvard

Date:February 28, 2018

Time:4:15 pm

Location:Pupin 428

Host:Lorenzo Sironi

The Event Horizon Telescope (EHT) is a global very-long-baseline interferometer operating at 1.3mm wavelength. The EHT currently achieves an angular resolution of ~10 microarcseconds -- comparable to the angular size of the Schwarzschild radius of the Galactic Center supermassive black hole, Sgr A*. Previous EHT observations of Sgr A* have demonstrated that the 1.3mm emission region subtends only a few Schwarzschild radii, and they have detected image asymmetry and substructure on these scales. The EHT also discovered ordered magnetic fields with vigorous activity near the event horizon. However, these past observations have lacked the sensitivity and baseline coverage to produce images. With the 2017 expansion to eight sites, including the ALMA array, the EHT now has the potential to directly image the black hole and its surrounding magnetic fields. I will discuss recent EHT progress and results, including the emerging capabilities of the EHT to study relativistic dynamics of accretion flows, to elucidate the role of magnetic fields in jet launching, and to track structural evolution during flares of Sgr A*.